The present invention relates to swath-type printers, and more particularly to a media advance system for precisely advancing the media after printing each swath to position the media for the next swath without overlapping the previously printed swath or leaving a gap between the successively printed swaths.
Swath-type printers are well known in the art. These printers use a print head having a plurality of print devices mounted thereon. Typically the print head is mounted on a carriage for translational movement along a carriage scan axis. The media, such as a paper sheet, is transported along a media advance axis by a media advance system. The media advance axis and the scan axis are orthogonal. Thus, the print head is driven back and forth along the scan axis to print the successive swaths, with the media advance system advancing the media between each successive swath.
Print heads employing various types of printing devices are known in the art. A common type of print head employs ink jet nozzles as the print devices. Thus, the print head may include a multiplicity of N ink jet nozzles aligned with respect to the media advance axis.
A particular problem with swath-type printers is the positioning of the media for printing of successive swaths. If the media is not advanced far enough, successive swaths will be printed over a portion of the preceding swath, creating an overlapping band. If the media is advanced too far between each swath, there will be a band between the successive swaths on which no information is printed. Such bands can be particularly objectionable if the printer is used for printing high resolution graphics for example.
The precision of advancement of the media is affected by the mechanical systems. The need for precise positioning of the media is increased when the printer is a high resolution printer used for printing graphics with high resolution.
To attempt to solve this problem, media advance systems have been employed which require accurate mechanisms to advance the media accurately enough to eliminate the banding caused by swath advance error. Such systems are expensive due to the relative high cost required for the accurate mechanical systems. Systems have also been proposed which employ CCD sensor arrays to monitor the movement of one individual line for the advance. Such systems are subject to precise adjustment of the sensor magnification effects (i.e., the object distance would have to be carefully controlled to a preset amount.) Other proposed schemes cannot adjust for print-module to print-module errors (i.e., different swath widths from module to module).